1)Does the weekly server-promotion cost affect how often my server appears in the suggested servers list? If i increase the promotion cost, will my server appear in the suggested servers list more often?

2) How does the weekly promotion cost for servers work? I know it somehow also changes the order of the servers as they appear in the lists, but how exactly? e.g., only within a country's list? what about in relation to the number of people a server has that moment, or the average rank of the people in it (green boxes etc)? what is more important?

General comment (related to the above): my server usually has 4-8 people, all from the country the server is placed in, but there are some moments when the server within just 2 minutes jumps to 20-25 people, from all different countries. Is this related to the weekly promotion cost and how?

1) Servers in "suggested" area are those where my friends are playing, or some (random?) ones with around 20 players

2) Servers are listed from the most "populated" to the least, and by players rankings range (for example, servers where players have all a very high rank (around a million let's say) will be after the ones with players with rank similar to me)

I see when not-very-popular servers, there are much players (like 25 in a server where usually there are 5/6, which would be pretty much your situation) it's because it became a server with "Red arrow" for you, and green box for newcomers, meaning it has only players that have a very few LP. In this situation, since servers with newcomers only are way less, more will join it.